The present invention relates generally to the manufacture of elbows for furnace pipe or the like, and more particularly, to an apparatus and method for cutting a sheet of material into a plurality of segments having curved edges.
In order to direct the flow of air or other gas to a desired location, conventional furnace pipe or similar ducts employ elbows for joining straight portions of the pipe. Typically, this pipe is made from a galvanized iron sheet which is closed at a longitudinal seam. In order to produce an elbow, one or more tubular segments must have ends which are cut at an angle relative to the axis of the pipe.
A variety of methods have been utilized for producing elbow segments with beveled ends. For example, one such method is to close the sheet metal to form a tube, mount an elliptical collar around the end of the tube, and revolve a cutter around the tube at the angle formed by the collar. Other devices, such as that disclosed in U.S. Pat. No. 4,054,069 to Coop, rotate and axially oscillate a tube relative to an angularly positioned cutter. Devices such as these which perform the cutting operation after the sheet metal is formed into a pipe tend to be expensive and inaccurate. It is difficult to control the angular positions of the pipe relative to the cutters and also time consuming to mount and cut one segment at a time.
Another method of cutting the ends of the tubular segments is to perform the cut on the sheet metal before it is closed into a tube. To create a closed tube with a beveled end shaped as an ellipse, a cut is made in the sheet metal in the form of a sinusoidal wave. Thus, a desired number of segments can be cut in such a manner, closed to form a tube with the desired beveled ends, and assembled together to form an elbow for joining straight segments of pipe.
One such machine which cuts the sheet metal prior to being formed into a tube has been manufactured and sold by Spiro, Inc. The Spiro machine uses a plurality of caster-like cutters which rotate freely about a vertical axis in response to movement of the sheet metal past the cutters. To make a desired cut, the cutters are moved in a lateral direction as the sheet metal moves in a longitudinal direction. The entire sheet of metal is cut into the desired segments when the sheet makes one pass past the cutters.
Another method of cutting the sheet metal prior to forming it into a tube is to use a plasma-type cutter to burn a cut into the sheet metal. These machines typically move the sheet in an X and Y direction while a flame burns into the metal. Such machines tend to produce elbow segments with rough edges or burrs. When assembling the elbow segments together after closing them into tubular segments, the burrs often bind or otherwise damage the assembly machines. Moreover, plasma-type cutters produce bad fumes and smoke, especially when used to cut galvanized metal.
Other attempts have been made to cut a desired pattern in paper or other thin sheet material. For example, U.S. Pat. No. 3,477,322 to Gerber et al. discloses a cutter head supported for movement above a work supporting surface and controlled in two dimensional movements by an associated automatic controller. A reciprocating tool is rotated about its axis of reciprocation during a cutting process to maintain the cutting edge tangent to the line of cut.